Bare TiO₂ and nominal 5.0 at% Fe-doped TiO₂
nanoparticles were synthesized by the modified sol-gel method. The
samples were physically characterized in order to obtain the correlation
 between structure and photocatalytic properties by X-ray diffraction
(XRD), scanning electron microscopy (SEM), transmission electron
microscopy (TEM), Brunauer, Emmett and Teller (BET), and UV-vis diffuse
reflectance spectrophotometry (UV-vis DRS). XRD results indicated that
phase structures of bare TiO₂ and Fe-doped TiO₂ nanoparticles were the mixture of anatase and rutile phases. The content of rutile phase in 5.0 at% Fe-doped TiO₂ nanoparticles decreased . TEM images revealed that the shape of bare and 5.0 at% Fe-doped TiO₂
 was almost spherical and the average particle size was in the range of
10-30 nm. Specific surface areas of the samples were found as 75 and 134
 m²/g for bare TiO₂ and nominal 5.0 at% Fe-doped TiO₂,
 respectively. The results from UV-vis reflectance spectra clearly
indicated the shift of absorption band edge towards visible region upon
doping TiO₂ with iron. Photocatalytic activity of bare TiO₂ and 5.0 at% Fe-doped TiO₂
 nanoparticles was examined by studying the mineralization of oxalic
acid under visible light irradiation and the results clearly showed that
 Fe-doped TiO₂ sample exhibited higher activity than bare TiO₂.